Holding Web for an Exhaust Gas Processing Unit, Associated Device, Production Method and Exhaust Line

ABSTRACT

The web ( 8 ) is arranged around a processing unit ( 14 ) between the processing unit ( 14 ) and an envelop ( 16 ) which defines a conduit ( 12 ) for the exhaust gas flow. The web ( 18 ) includes a mattress whose external side is provided with an aluminosilicate-containing coating ( 30 ). The invention is used for motor vehicle exhaust lines.

The present invention relates to a support sheet for supporting a member for treating exhaust gas from an engine, the sheet being for placing around the treatment member between the treatment member and a casing defining an exhaust gas flow duct, the sheet comprising a mat presenting an external coating.

In order to depollute an engine, in particular motor vehicle diesel or gasoline engines, it is known to fit the exhaust system with one or more gas treatment devices, in particular devices for providing catalytic treatment and/or devices that incorporate particle filters.

The treatment member, which depending on circumstances may be constituted by a particle filter or by a catalytic purification member, is disposed in a gas flow duct defined by an outer casing. In order to ensure that the treatment member is held in place, regardless of expansion conditions, it is known to interpose an intermediate sheet between the treatment member and the casing. This sheet may be of the intumescent type (Ibiden 100 or XPEAV2 for example), or of the non-intumescent type (Ecoflex 200™ or Flec N263™, for example).

The sheet serves firstly to hold the treatment member transversely relative to a longitudinal axis of the casing, and secondly to hold said member axially by being held tightly inside the casing.

Such devices do not give entire satisfaction. Under the action of exhaust gas, the sheet erodes during use of the exhaust system, and that can be harmful to the treatment member being held inside the casing.

A main object of the invention is thus to provide a support sheet that ensures that the treatment member is held inside the casing in reliable manner throughout prolonged utilization of the device.

To this end, the invention provides a sheet of the above-specified type, characterized in that the coating comprises an aluminosilicate.

In particular embodiments, the sheet includes one or more of the following characteristics:

-   -   the aluminosilicate comprises an alumina silicophosphate;     -   the aluminosilicate comprises 40% to 60% by weight silicon         oxide, 10% to 30% by weight phosphorous oxide, and 10% to 30% by         weight aluminum oxide, relative to the total weight of         aluminosilicate;     -   the aluminosilicate further comprises 5% to 10% by weight sodium         oxide and/or potassium oxide and 0.5% to 2% by weight iron oxide         relative to the total weight of aluminosilicate;     -   the aluminosilicate comprises a poly(silicon-oxo-aluminate)         presenting motifs having the general formula:         M_(n)[—(SiO₂)_(a)—AlO₂—]_(n)         in which:

n is an integer greater than 1;

a is an integer in the range 1 to 30; and

M is a cation selected from Na⁺, K⁺, Li⁺, Ca²⁺, Ba²⁺, H₃O⁺, and mixtures thereof; and

-   -   the coating can be obtained by a method of applying an aqueous         dispersion on the body of the sheet, the aqueous dispersion         presenting a dry extract lying in the range 20% to 50%.

The invention also provides a device for treating engine exhaust gas, the device being characterized in that it comprises:

-   -   a casing defining an exhaust flow duct;     -   at least one treatment member disposed in the duct; and     -   a sheet as defined above, the sheet being disposed between the         treatment member and the casing, around the treatment member.

In particular embodiments, the device includes one or more of the following characteristics:

-   -   the sheet has an upstream transverse face and a downstream         transverse face, both substantially perpendicular to a         longitudinal axis of the treatment member, at least one of the         upstream and downstream transverse faces presenting said         coating; and     -   the sheet presents two side faces bearing respectively against         the casing and the treatment member, at least one of the side         faces presenting said coating.

The invention also provides a method of manufacturing a device as described above, the method being characterized in that it comprises the steps of:

-   -   coating a face of the sheet at least in part using a binder         comprising an aluminosilicate in order to form a coating;     -   applying the sheet against the treatment member; and     -   placing the treatment member and the sheet in the casing.

The method may further include the following characteristic:

-   -   the face is coated by spraying on the binder.

The invention also provides an exhaust system, characterized in that it includes a device as defined above.

The invention can be better understood on reading the following description given purely by way of example and made with reference to the accompanying drawing, in which:

FIG. 1 is a longitudinal section view of a first treatment device of the invention, and

FIG. 2 is a view analogous to FIG. 1 showing a second device of the invention.

FIG. 1 shows a device 10 for treating exhaust gas, the device forming a segment in an exhaust system of a vehicle driven by an engine, such as a diesel-engined vehicle. The segment comprises an exhaust volume 12 containing a first treatment member 14 such as a catalytic purification member or a particle filter.

The exhaust volume 12 is defined by a cylindrical casing 16 defining a flow passage for exhaust gas. The ends of the cylindrical casing 16 are extended by a converging segment and by a diverging segment, where converging and diverging are to be understood relative to the gas flow direction in the exhaust volume.

Below, the terms “upstream” and “downstream” should be understood as being relative to the flow direction of exhaust gas through the casing 16.

An intermediate sheet 18 made of an intumescent material (XPEAV2™ from Unifrax) is interposed between the treatment member 14 and the cylindrical casing 16. This sheet is constituted, for example, by a mat of interlaced ceramic fibers, or fibers that are joined to one another by an inorganic or an organic binder.

The thickness of the sheet 18 is about 3 millimeters (mm).

The generally cylindrical casing 16 presents a cone 20 downstream from the treatment member 14, which cone defines internally a shoulder against which the sheet 18 bears in order to retain the treatment member 14 axially. In particular, the outside section of the treatment member 14 is greater than the inside section of the casing 12 beyond the cone 20.

A second treatment member (not shown) can be provided in the casing 16, downstream from the first member 14. Depending on circumstances, it may be a catalytic purification member or a particle filter. It is arranged, and in particular retained, in the same manner as the first member 14, by means of a peripheral sheet.

As shown in FIG. 1, the sheet 18 is generally tubular in shape, e.g. rectangular. It is suitable for being wound around the treatment member 14. Its cross-section is thus of a shape that is complementary to the outside cross-section of the treatment member 14.

The sheet 18 presents an inside face 22 and an outside face 24 bearing respectively against an outside surface of the treatment member 14 and against an inside wall of the cylindrical casing 16. The sheet 18 also presents, at each end, an upstream annular transverse face 26 and a downstream annular transverse face 28, both substantially perpendicular to a longitudinal axis X-X′ of the treatment member 14.

In the example shown in FIG. 1, the inside face 22 and the outside face 24 present respective surface coatings 30 comprising an aluminosilicate.

The aluminosilicate-based coating 30 increases the coefficient of friction firstly between the outside face 24 of the sheet 18 and the casing 16, and secondly between the inside face 22 and the treatment member 14. Furthermore, the coating 30 maintains the cohesion of the sheet 18, particularly when the sheet is made up of interlaced fibers without any inorganic or organic binder.

The thickness of the coating 30 measured along an axis perpendicular to the longitudinal axis X-X′ is less than 2 mm, and preferably lies in the range 50 micrometers (μm) to 1 mm.

The coating 30 on the inside and outside faces 22 and 24 is continuously. In a variant, it could present internal pores.

The term “aluminosilicate” designates a substance comprising oxides of silicon and oxides of aluminum, preferably chemically bonded together, as described below.

The aluminosilicate preferably comprises an alumina silicophosphate. In the example shown, the alumina silicophosphate comprises 40% to 60% by weight silicon oxide, 10% to 30% by weight phosphorous oxide, and 10% to 30% by weight aluminum oxide, relative to the total weight of the aluminosilicate in the coating 30.

In addition, the alumina silicophosphate contains 5% to 10% by weight sodium oxide and/or potassium oxide and 0.5% to 2% by weight iron oxide relative to the total weight of aluminosilicate in the coating.

The coating preferably comprises an inorganic polymer material of the poly(silicon-oxo-aluminate) type also known as “poly(sialate)”.

This type of inorganic polymer has a lattice made up of SiO₄ and AlO₄ tetrahedra bonded together in alternation by atoms of oxygen. The lattice may be two-directional or three-directional.

Furthermore, the aluminum in the lattice has a coordination number of IV.

Cations selected from alkalis, alkaline earths, or other cations, are present in the structural cavities defined by the lattice in order to balance the negative charge of the aluminum with coordination number IV. The cations are preferably selected from the group constituted by Na⁺, K⁺, Li⁺, Ca²⁺, Ba²⁺, H₃O⁺, and mixtures thereof.

Thus, the poly(sialate) presents motifs having the general formula: M_(n)[—(SiO₂)_(a)—(AlO₂)—]_(n)  (1) in which:

n is an integer greater than 1;

a is an integer in the range 1 to 30; and

M is a cation selected from Na⁺, K⁺, Li⁺, Ca²⁺, Ba²⁺, H₃O⁺, and mixtures thereof.

Preferably, the molar ratio between silicon and aluminum in the aluminosilicate is greater than 3, and lies in the range 3 to 6.

This type of poly(sialate) is obtained, for example, by a method of polymerizing a basic mixture comprising a powder of silicate and aluminosilicate and a strongly alkaline aqueous solution of soluble silicate.

The powder of silicate and aluminosilicate comprises, for example, an aluminosilicate oxide powder of composition lying in the range (2SiO₂, AlO₂) to (40SiO₂, AlO₂).

The highly alkaline aqueous solution of silicate, presents, for example, an M₂O/SiO₂ molar ratio lying in the range or equal to 0.5 to 1, in which M₂O is either sodium oxide, or potassium oxide, or a mixture of sodium oxide and potassium oxide.

The metallic oxide, preferably selected from an aluminosilicate, an iron phosphate, a copper phosphate, a zinc phosphate, and mixtures thereof, is preferably added to the basic mixture before polymerization.

Examples of poly(sialate) and of a method of obtaining such poly(sialates) or less are described, for example, in French patent application FR 2 838 733.

The coating 30 is preferably obtained by applying an aqueous dispersion of alumina silicophosphate on the sheet 18, as described below.

This aqueous dispersion presents a dry extract lying in the range 20% to 50%.

The term “dry extract” designates, for a given sample of aqueous dispersion, the ratio between the weight of dry matter that remains after the sample has been dried in an oven at a temperature greater than 100° C., and the initial weight of the sample prior to drying.

In the example shown in FIG. 2, the aqueous dispersion of alumina silicophosphate applied to the sheet 18 in order to form the coating 30 is the binder Geopolymite® CT AB 04 from the French supplier Geopolymère. The binder possesses a dry extract of 35% and an oxide composition as specified in the table below. Oxide Content (%) SiO₂ 48.8 P₂O₅ 20.7 Al₂O₃ 22.2 Na₂O 7.4 Fe₂O₃ 0.9

A method of making the device 10 shown in FIG. 1 is described below by way of example.

Initially, the inside and outside faces 22 and 24 of an intumescent sheet 18 of the XPEAV2™ type from the supplier Unifrax are coated by an aqueous dispersion of the binder Géopolymite® CT AB 04.

The coating may be performed by dipping the sheet 18 in a receptacle containing the binder or by spraying the binder on the faces of the sheet 18. Dipping enables all of the faces of the sheet 18 to be coated, whereas spraying enables coating to be performed selectively on one or more faces of the sheet 18.

The method then comprises a heat treatment step in an oven at 120° C. for one hour. In a variant, the heat treatment step could be omitted.

The coating formed in this way presents a thickness of less than 10 mm.

The sheet 18 is then wound around the treatment member 14, pressing against the outside surface of the member 14.

Thereafter, the assembly constituted by the treatment member 14 and the sheet 18 is inserted by force into the casing 16. The sheet 18 and the treatment member 14 are held inside the casing 16 by being held tightly therein.

As specified above, the coating 30 based on aluminosilicate increases the coefficient of friction firstly between the outside face 24 of the sheet 18 and the casing 16, and secondly between the inside face 22 and the treatment member 14. Consequently, any movement of the treatment member 14 relative to the casing 16 along the longitudinal axis X-X′ is greatly restricted, even if the pressure of exhaust gas downstream from the treatment member 14 is high.

Furthermore, the coating 30 provides cohesion between the fibers forming the sheet 18, particularly if the sheet does not have any inorganic or organic binder.

The physical and chemical properties of the sheet 18 are thus maintained for a long duration of use, at the utilization temperatures of the exhaust system, e.g. lying in the range 400° C. to 800° C.

In the second device 40 of the invention, shown in FIG. 2, the coating 30 based on aluminosilicate is placed on the annular upstream and downstream faces 26 and 28 of the sheet 18.

In this variant, the coating 30 is substantially continuous and thus prevents exhaust gas from penetrating into the sheet 18, thereby limiting chemical degradation thereof.

The method of making this second device 40 differs from the first method of the invention by the step of coating the annular faces 26 and 28 of the sheet 18, which step is performed after the treatment member 14 and the sheet 18 have been inserted inside the casing 16. Under such circumstances, the coating presents a thickness that is less than or equal to about 10 mm.

The presence of the coating 30 makes it possible, at lower cost, to keep the treatment member 14 in position relative to the casing 16 in durable manner, by protecting the sheet 18 against erosion.

In a variant, all of the external faces 22, 24, 26, and 28 of the sheet 18 presents a coating 30 comprising an aluminosilicate. 

1-12. (canceled)
 13. A support sheet for supporting a member for treating exhaust gas from an engine, the sheet being for placing around the treatment member between the treatment member and a casing defining an exhaust gas flow duct, the sheet comprising a mat presenting an external coating; wherein the coating comprises an aluminosilicate.
 14. A sheet according to claim 13, wherein the aluminosilicate comprises an alumina silicophosphate.
 15. A sheet according to claim 13, wherein the aluminosilicate comprises 40% to 60% by weight silicon oxide, 10% to 30% by weight phosphorous oxide, and 10% to 30% by weight aluminum oxide, relative to the total weight of aluminosilicate.
 16. A sheet according to claim 13, wherein the aluminosilicate further comprises 5% to 10% by weight sodium oxide and/or potassium oxide and 0.5% to 2% by weight iron oxide relative to the total weight of aluminosilicate.
 17. A sheet according to claim 13, wherein the aluminosilicate comprises a poly(silicon-oxo-aluminate) presenting motifs having the general formula: M_(n)[—(SiO₂)_(a)—(AlO₂)—]_(n) in which: n is an integer greater than 1; a is an integer in the range 1 to 30; and M is a cation selected from Na⁺, K⁺, Li⁺, Ca²⁺, Ba²⁺, H₃O⁺, and mixtures thereof.
 18. A sheet according to claim 13, wherein the coating can be obtained by a method of applying an aqueous dispersion on the body of the sheet, the aqueous dispersion presenting a dry extract lying in the range 20% to 50%.
 19. A device for treating engine exhaust gas, the device comprising: a casing defining an exhaust flow duct; at least one treatment member disposed in the duct; and a sheet according to claim 13, the sheet being disposed between the treatment member and the casing, around the treatment member.
 20. A device according to claim 19, wherein the sheet has an upstream transverse face and a downstream transverse face, both substantially perpendicular to a longitudinal axis of the treatment member, at least one of the upstream and downstream transverse faces presenting said coating.
 21. A device according to claim 19, wherein the sheet presents two side faces bearing respectively against the casing and the treatment member, at least one of the side faces presenting said coating.
 22. A method of manufacturing a device according to claim 19, the method comprising the steps of: coating a face of the sheet at least in part using a binder comprising an aluminosilicate in order to form a coating; applying the sheet against the treatment member; and placing the treatment member and the sheet in the casing.
 23. A method according to claim 22, wherein the face is coated by spraying on the binder.
 24. An exhaust system, including a device according to claim
 19. 